This invention relates to a gaseous sample concentration device that, upon analyzing a gaseous or liquid sample composed of multiple components using an apparatus such as a gas chromatograph, concentrates the gaseous sample at a certain position in the gas transfer line that transfers the gas into the apparatus.
Description of the Related Art
Apparatus, such as gas chromatographs, are available for analyzing gaseous or liquid samples composed of multiple components by introduction of such gas or liquid samples into a detector via a gas transfer line.
The gas chromatograph unit analyzes a gaseous sample composed of multiple components, first by injecting the sample using a micro-syringe or the like into a sample injection port located at one end of a separation column such as a capillary column or the like housed in a constant temperature chamber, then by separating the sample into each component in the separation column, and by detecting each separated component using a detector located at the other end of the separation column. The detector that is typically employed is a mass spectrometer or hydrogen flame ionization detector. Using the gas chromatograph, a gas chromatogram showing peaks to indicate the detection intensity (concentration) of each component along with corresponding retention times can be obtained as a result of this analysis.
For improving accuracy of the analysis, it is desirable when using the gas chromatograph that a single component be detected by a single isolated peak, and not be broken into multiple peaks. For this, it is required that the gaseous sample be introduced at the narrowest volume possible at the end of the separation column. In order for the gaseous sample injected into the separation column in the gas chromatograph to be concentrated within the narrowest possible volume, a conceivable method is to inject a required amount of the sample with a micro-syringe or the like. However, in the case that the concentration of the sample is very low, a large amount of sample, for example a few ml, needs to be injected. This is time-consuming and, therefore, is not at all a practical process to be implemented. Another conceivable method is to cool the entire column to a temperature below the ambient temperature so that the sample injected in the column becomes condensed and concentrated. This method, on the other hand, requires a large amount of refrigerant. Also, as the minimum attainable temperature is only -80.degree. C., trapping of low boiling-point compounds, such a hydrocarbons with carbon numbers less than 10, is almost impossible.
There is a conventionally known method wherein a portion of one side of the separation column to which the sample is introduced is wound in a coil and is cooled by dipping it into liquid nitrogen placed in a Dewar vessel. In this method, after the gas sample is condensed within that portion, the separation column is taken out of the Dewar vessel and is placed in a constant temperature chamber. By these processes, the temperature inside of the separation column is raised and the condensed sample desorbs thermally, and the components of the sample are further separated from each other by the separation column.
This method can almost perfectly condense and trap a sample consisting of multiple components having carbon numbers of greater than 3 or 4 (i.e., propane or butane in the case of hydrocarbon) at the cooled portion. As a result, each component that is trapped thereby is detected by a single peak.
The above-described method can be practiced in the laboratory. However, implementing it is still cumbersome due to the fact that all the steps usually have to be carried out manually, since it has proven difficult to automate the method.
In order to solve the aforementioned problem, a method can be considered in which a nozzle for spraying liquid nitrogen is placed facing a portion of the separation column in the neighborhood of the sample injection port, whereby the portion of the separation column is directly cooled with liquid nitrogen that is sprayed from the nozzle. By this method, the portion of the separation column can be locally cooled to the temperature of liquid nitrogen (-196.degree. C. ) within a constant temperature chamber which is otherwise kept at a desired temperature, 40.degree. C. for example. It is therefore expected that the sample injected into the sample injection port can be condensed at the cooled portion of the column and that each component can be detected as a corresponding single peak.
However, upon cooling by liquid nitrogen using this method, moisture in the air condenses and freezes around the cooled portion of the separation column, and after the nitrogen spray stops, the air inside the constant temperature chamber enters into the nozzle and moisture existing in the air freezes into ice inside of the nozzle. This will create a problem in that the open end of the nozzle becomes plugged up with ice, making subsequent sprays of the liquid nitrogen difficult.